The present invention relates to a sound generating device for automatically generating sound, in particular to a sound generating device which generates a melody by storing a variety of sound data in a storing circuit and successively reading this data from the storing circuit.
A conventional sound generating device is known in the art as shown in FIG. 1 and includes an oscillator 91 for providing a clock signal output. A note length generating circuit 92 variably divides the clock signal. A main ROM 93 stores data relating to note length and note scale for each note of a melody. Note length data is read from main ROM 93 into note length generating circuit 92 to determine a division ratio for dividing the output clock signal. The divided clock signal is input to a main counter 95 which in turn controls the incremental reading of the addresses of main ROM 93 in accordance with the note length.
Similarly a note scale generating circuit 94 reads note scale data from main ROM 93 and determines the division ratio for dividing the output of oscillator 91. Note scale generating circuit 94 variably divides the clock signal supplied by oscillator 91 in accordance with the calculated division ratio to output a clock signal having a frequency based upon the note scale of the note to be used in the melody. An envelope generating circuit 96 receives the divided clock signal from note scale generating circuit 94. Envelope generating circuit 96 is formed of a capacitor C and a resistor R. Envelope generating circuit 96 forms an analog wave having a predetermined shape by discharging the charge from the charged capacitor through the resistor in response to timing of the signal applied to it. The signal from note scale generating circuit 94 to which the envelope is added is supplied to a speaker so that a sound having a note scale corresponding to data stored in main ROM 93 is generated for a time period corresponding to the note length. By successively reading data from main ROM 93, a melody may be automatically produced.
This sound generating device has been satisfactory. However, the conventional sound generating device is limited to sound waveforms formed strictly as rectangular waves or waveforms wherein an exponentially curved envelope formed by a CR envelop generator is added to the rectangular wave. Therefore, tone quality deteriorates to an extent that the conventional device may only be used for sounds such as those produced by or used during the hold telephone period, melody cards or the like. Additionally, the prior art sound generating devices provide a uniform sound devoid of any sound accenting. Accordingly, the prior art sound generating devices suffer from the inability to produce a great variety of sounds, generate sound rhythms, natural sounds, stereo sounds and profound sounds. Accordingly, it is desired to provide an apparatus for generating sound which overcomes the shortcomings of the prior by providing a sound generator capable of producing a wide variety of sounds.